You only want to use enough vinegar to dissolve your AMT. Otherwise you are going to have an arse like a gunshot wound. You should titrate (ie drip) vinegar into a mixure of say 5-10ml water and your AMT. Stir as you drip a few drips and gradually the AMT will disslove. Go slow and give it a chance to dissolve between drips. That way you will use the minimal quantity of vinegar and reduce the likely incidence of embarrassing complication.
Of course if you have the salt, you don't need to be asking this question but I'm sure you already knew that.
Incidentally this route of ingestion does not necessarily reduce nausea in my experience. I tended to parachute it into a nearly emptly stomach and maybe eat something later when the onset has come and gone.
I haven't heard much about vaping the freebase, although Tihkal has some reports. They mention rapid onset, similar duration but do not mention nausea.
I had a gram a few years back and dabbled over that year. It has a nice afterglow, but I am not sure if I overall really liked it a lot. It was the perhaps slightly stimulant features combined with genereal tummy unease which sometimes tainted the otherwise pleasant and euphoric headspace.